Bio-fouling is the buildup of micro and macro organisms on all materials that are immersed in natural bodies of water (Yebra et al., 2004). Contending with biofouling has been a challenging problem since the beginning of navigation (Hellio and Yebra, 2009). Extensive and rapid buildup of fouling on the ship hull cause reduction in ship speed and maneuverability which in turn increases operating costs and environmental penalties (Magin et al., 2010; Callow and Callow, 2002). In the medieval age, copper and lead sheathing covering the ship hulls were used as the primary method of controlling biofouling (Hellio and Yebra, 2009). Advancement in polymer and resin technology in the 1960's led to the use of self-polishing copolymers with controlled release of biocides such as Tributyl tin (TBT), (Yebra et al., 2004; Hellio and Yebra, 2009). However, by the 1970s, deleterious effects of TBT towards aquatic life started to appear. The International Maritime Organization addressed the issues of TBT by placing restrictions that later established protocols for complete prohibition of tin based antifouling paints in 2003 (Yebra et al., 2004). Antifouling technologies using copper oxide as biocide had been used previously and is now the predominate biocide used in commercial antifouling coatings (Konstantinou and Albanis, 2004). Due to concerns regarding the release of biocides into the environment, a considerable amount of research has been carried out towards using non-toxic anti-fouling (AF)/fouling release (FR) technologies that are environmentally friendly (Lejars et al., 2012).
Fouling release coatings systems primarily consist of silicone elastomers which allow only the weak attachment of fouling organisms which are removed due to hydrodynamic forces (Lejars et al., 2012). However these silicone based fouling release coatings have some drawbacks such as deterioration of fouling release properties over time and poor mechanical durability compared to anti-fouling coatings with controlled release of biocides (Yebra et al., 2004; Lejars et al., 2012). Siloxane polyurethane fouling release coatings developed by Webster and coworkers have been able to address the issues with durability by incorporating polydimethyl siloxane (PDMS) in to a polyurethane matrix (Webster and Ekin, 2010; Webster et al. 2011). Self-stratification PDMS provides the FR properties on par with commercial FR coatings and polyurethane bulk provides mechanical performance that is a magnitude higher than silicone elastomers (Ekin and Webster, 2006; Bodkhe et al., 2012b; Sommer et al. 2010). Unlike silicone elastomer-based FR coatings, siloxane polyurethane coating systems have excellent adhesion to primers which eliminates the need for a separate tie-coat (Bodkhe et al., 2012b).
Adhesion of marine organisms to surfaces is a complex phenomenon (Yebra et al., 2004; Hellio and Yebra, 2009). However, the primary method of adhesion involves spreading of an adhesive that consists of complex protein or glycoprotein (Iguerb et al., 2008). Therefore, materials modified with polyethylene glycol (PEG) are of great interest mainly due to their ability to resist protein adhesion (Wyszogrodzka and Haag, 2009). Self-assembled mono layers (SAM) containing PEG are commonly used as protein resistant materials (Wyszogrodzka and Haag, 2009; Szleifer 1997). However, SAMs are not practical for use as marine coatings (Prime and Whitesides, 1993). Polyurethanes modified with PEG, on the other hand, have demonstrated their versatility in biomedical applications, and surface domination of PEG plays a key role in protein resistance.
In previous attempts to modify siloxane polyurethanes with polyethylene glycol, amino propyl-terminated siloxane with pendent PEG chains provided amphiphilic coatings with improved algae removal compared to 1st generation siloxane polyurethane coatings (Bodkhe, 2011). However, the synthesis of polydimethyl siloxane with pendent PEG chains involves multiple steps.